ICEs include one or more camshafts that open and close intake/exhaust valves and are rotationally driven by a crankshaft via an endless loop, such as a chain. The camshafts have shaped lobes that open and close valves as the camshafts are rotated. The opening and closing of the valves is precisely controlled based on the angular position of the camshaft(s) relative to the angular position of the crankshaft. In the past, the angular position of the crankshaft was fixed relative to the angular position of the camshaft(s). However, the ability to change the angular position of the camshaft relative to the angular position of the crankshaft such that ignition timing is advanced or retarded can help increase engine performance in a variety of ways, such as by improving engine smoothness as low-operating temperatures. The ability of change the angular position of the camshaft relative to the angular position of the crankshaft is often referred to as VCT.
VCT can be implemented in a variety of ways. For example, VCT can be implemented using camshaft phasers that are actuated electrically or hydraulically. With respect to hydraulically-actuated camshaft phasers, a stator receives a rotor having one or more vanes. The stator can include a camshaft sprocket that engages the endless loop and communicates rotational energy from a crankshaft sprocket that also engages the endless loop. The rotor can include one or more vanes and be received by chambers formed in the stator so that a radially-outward end of the vane abuts a radially-inward facing surface of the chamber to divide the stator into an advancing chamber section and a retarding chamber section. Supplying fluid, such as engine oil, to a first chamber while permitting fluid to exit a second chamber can move the rotor in one angular direction relative to the stator. The rotor can be moved in another angular direction if fluid is supplied to the second chamber and emptied from the first chamber. Various mechanisms exist for supplying this fluid. For example, an oil-pressure actuated (OPA) camshaft phaser can use fluid can be supplied to the chamber from an oil-pump included with the ICE that pressurizes fluid for supply to the camshaft phaser. The pressurized fluid can then be directed to the advancing chamber section or the retarding chamber section. However, it would be helpful to control the supply of fluid to the chambers without using a separate oil pump to pressurize the fluid.